Tin-phoshorus catalyzed oxidative dehydrogenation

ABSTRACT

THE ACTIVITY OF TIN-PHOSPHORUS OXIDATIVE DEHYDROGENATION CATALYSTS IS SIGNIFICANTLY IMPROVED BY INCLUDING A HEATVOLATILE ACTIVITY-STIMULATING AMMONIUM SALT IN THE CATALYST COMPOSITION PRIOR TO THE CATALYST PARTICLE-FORMING STAGE.

United States Patent 3 775 508 TIN-PHOSPHORUS CATALYZED OXIDATIVE DEHYDROGENATION Emory W. Pitzer, Bartlesville, 0kla., assignor to Phillips Petroleum Company No Drawing. Filed Apr. 16, 1971, Ser. No. 134,880

Int. Cl. C07c /18 US. Cl. 260-680 E 10 Claims ABSTRACT OF THE DISCLOSURE The activity of tin-phosphorus oxidative dehydrogenation catalysts is significantly improved by including a heatvolatile activity-stimulating ammonium salt in the catalyst composition prior to the catalyst particle-forming stage.

BACKGROUND OF THE INVENTION This invention relates to an improved oxidative dehydrogenation catalyst. The invention further relates to a dehydrogenation process utilizing the improved catalyst composition.

Oxidative dehydrogenation catalysts can be formed from a phosphorous component, a tin component, and, optional ly as well as preferably, at least one of a Group Ia or IIa metal or metal-containing material. However, improving the activity of such catalysts is highly desirable.

SUMMARY OF THE INVENTION According to my invention, a catalyst composition is formed from the combination of a phosphorus-containing material, a tin-containing material, and optionally as Well as preferably at least one of a Group Ia or IIa metal or metal-containing material, more preferably a lithium component, further together with a heat-decomposable heatvolatile activity-stimulating ammonium salt which is added to the catalyst composition prior to the final particleforming or shaping step. The resulting catalyst composition exhibits substantially improved oxidative dehydrogenation activity.

It is an object of my invention to provide an improved tin-phosphorus oxidative dehydrogenation catalyst. It is another object of my invention to increase the activity of tin-phosphorus oxidative dehydrogenation catalysts. A further object of my invention is to improve the yield of desired product in oxidative dehydrogenation processes.

Other aspects, objects, and the several advantages of my invention will become further apparent to those skilled in the art upon the consideration of my disclosure and claims.

DETAILED DESCRIPTION OF THE INVENTION The inclusion of a heat-decomposable heat-volatile activity-stimulating ammonium salt in preparation of tinphosphorus oxidative dehydrogenation catalyst compositions significantly improves the effective activity of the catalysts.

In preparing my catalysts, I use a phosphorus-containing material, plus a tin-containing material, plus optionally and preferably a Group Ia or Ila metal or metal-containing material, together with the additive of my invention which is a heat-decomposable heat-volatilizable activitystimulating ammonium salt, preferably a halogen-free ammonium salt, which is added at one or more appropriate preparation stages.

This activity-increasing component can be added to the catalyst composition at any stage prior to that of forming or shaping the catalyst particles such as by pelletizing, extrusion, or the like. The additive can be added during the very first precipitation or gel-forming step without subsequent washing; or the addition can be at a wet gel stage prior to drying which is my presently preferred method; or the addition can be after a gel-drying stage but prior to catalyst-shaping.

These heat-decomposable heat-volatile activity stimulating ammonium salts include those which will not otherwise deleteriously affect the oxidative dehydrogenation activity and capacity of the tin-phosphorus oxidative dehydrogenation catalyst compositions. Suitable ammonium salts include the carbamate, carbonate, nitrate, nitrite, sulfate, as well as ammonium salts of carboxylic acids having up to about 12 carbon atoms per molecule including such as the formate, the hydrogen acetate, propionate, lactate, benzoate, succinate,'phenolate, dodecanoate, and the like, in any of the various hydrated or partially hydrated as well as anhydrous forms, as well as mixtures, or combinations such as the carbamate acid carbonate often known as sal volatile.

Suitable phosphorus-containing materials include phosphoric acid, phosphorous oxide such as pentoxide or trioxide, phosphorous triand penta-halides such as phosphorous pentachloride, the Group Ia alkali metal phosphates and the Group Ila alkaline earth metal phosphates of lithium, sodium, potassium, rubidium, cesium, magnesium, and calcium, and including the various phosphate forms such as ortho-, meta-, pyro-, polysuch as hexametaphosphate, and the like, as well as mixtures.

Useful tin-containing materials include any which are soluble or dispersable in water, or in other solvent such as alcohol or ether, and include both the stannous and stannic compounds such as the stannic halides, including stannic or stannous, such as the fluoride, chloride, bromide, iodide, as well as other salt such as sulfate, acetate, oxide, nitrate, and carboxylate such as the tartrate, and the like, as Well as mixtures.

The optional though preferred Group Ia or Ila component, which additional component appears to assist length of operation of the catalyst before regeneration, can be the metal itself including lithium, sodium, potassium, rubid1um, cesium, beryllium, magnesium, calcium, strontium, barium, or can be a Group =Ia or IIa metal-containing material such as the corresponding nitrate, halide including fluoride, chloride, bromide, iodide, the sulfate, oxalate, carbonates, bromates, oxides, hydroxides, and carboxylates such as acetates, propionates, tartrates, and the like, as well as mixtures. The more preferred alkali or alkaline earth metal component is lithium or a lithium-containing compound.

The phosphorus-containing material, the tin-containing material, and the optional Group Ia or 1111 metal or metalcontaining material, are combined in any conventional manner to yield active catalyst combinations suitable for oxidative dehydrogenation processes. For example, the several components can be combined using a coprecipitation gel-forming technique from aqueous or non-aqueous solutions or dispersions or suspensions, to which, if desired, minor amounts of an alkaline material can be added for gel pH adjustment; or even by intimate mixing of the components themselves without the use of additional solvents; and the like.

The concentration of the various solutions or dispersions that can be used to make my catalyst compositions can vary over wide ranges, from about 0.01 to 10 molar or more, depending on the solubility of the particular materials employed, and the particular solvent or mixture of solvents utilized. Suitable solvents or dispersants that can be employed for the combining of the several components include water, the lower alcohols, the lower ethers, hydrocarbons, ketones, esters, and the like.

Any order of mixing can be used. Generally, the catalyst compositions are formed by mixing the several components, prior to addition of my activity-stimulating salt, for intervals varying from about 1 minute to 5 hours or more in the presence or absence of a solvent or dispersant, at temperatures of about room temperature, or even less with the organic solvents, up to around 200 F., again depending upon the presence or absence of the solvent and the type thereof. Pressures ranging from less than to much greater than atmospheric pressures can be utilized. If desired, inert atmospheres can be employed, such as nitrogen. The final pH of the mixture generally is in the range of about 2 to 10. The precipitate, i.e., the gel, that forms is separated from the liquid by any conventional means such as by filtration, decantation, and the like. Thereafter, the precipitate can be washed, if desired, to remove any undesirable electrolytes, using water, including softened or deionized water as may be convenient.

Optionally, and preferably, the Group IA or IIa, preferably lithium, component can be added after the catalyst particle has been shaped, more preferably even after calcination. Thus, the finished calcined pellet containing tin, phosphorus, and corresponding oxygen, is given a final impregnation with a soluble alkali or alkaline earth metal compound, preferably lithium, and calcined again.

The heat-decomposable heat-volatile activity-stimulating ammonium salt additive can be intimately mixed with or combined with the other materials, such as in the coprecipitation technique into a catalyst composition gel.

The presently preferred method of preparation comprises first forming a catalyst base containing the tin-containing component and the phosphorus-containing component, combined by such as precipitation techniques which result in a wet gel intermediate, and adding my activitystimulating additive to the washed wet gel as an aqueous or other solution, or by intimately dispersing a finely divided ammonium salt into the wet gel. The additive can be added before or after washing the gel. Of course, when the heat-decomposable heat-volatile activity-stimulating ammonium salt is added before the washing step, then such washing step should be omitted so as to avoid washing out of the activity-stimulating additive.

The intimate mixing can be obtained by any conventional mixing device. The amount of added activity-stimulating ammonium salt is in the range of about 0.5 to 20, preferably about 2 to 20, weight percent based on the final weight of the catalyst composition.

The catalyst compositions when finished and ready for use, such as in an oxidative dehydrogenation process, contain about 0.1 to 16 weight percent phosphorus, about to 75 weight percent tin, and about 0.1 to 10, preferably 0.1 to 5, weight percent of the Group Ia or IIa metal, and balancing amounts of oxygen, each expressed as the element and based on the total weight of the final catalyst composition. The amounts of phosphorus, tin, and Group Ia or Ila metal present in the final catalyst composition together total less than 100 percent based on the total weight of the catalyst composition, The difference between the total weight and 100 percent being substantially combined oxygen in an amount sufficient to satisfy the valence combining requirements of the Group Ia or IIa metal, the tin, and the phosphorus, components.

The wet gel, including the heat-decomposable heat-volatile activity-stimulating salt, when added at this stage which I find preferable according to my invention, is dried by any convenient methods and under any convenient conditions such as are sufiicient to reduce the moisture in the mixture to less than about 10 weight percent. Temperatures employed should be insufiicient to prematurely decompose the activity-stimultaing component. Usually, the drying can be carried out at temperatures up to about 350 F. The drying can be in air, or in the presence of an inert atmosphere such as nitrogen. If desired, the ammonium salt can be added after the drying step either as a solution or dispersion followed by further drying;

can be added by intimate mixing of a finely divided ammonium salt.

A minor amount of a lubricant frequently is added to the dried composition to assist in pelletizing catalyst compositions. The lubricant usually is a powdered polyolefin, frequently a powdered polyethylene, such as disclosed by Pitzer et al. in U.S. Letters Patent 3,051,662. On calcination, the lubricant is decomposed and volatilized along with other materials which are heat-decomposable.

The dried catalyst composition is formed into particles by means of pelletizing, extrusion, and the like. The final catalyst usually is in the form of pellets of to /z-inch, or granules in a 10 to 28 mesh range as defined by the U.S. Standard sieve series. The catalysts can be employed as such, or with suitable supporting or diluting materials such as alumina, eta-, gammaor alpha-alumina or mixtures thereof, boria, berylia, magnesia, titania, zirconia, and the like.

The dried, formed precipitate is calcined under conditions suflicient to substantially remove the heat-decomposable heat-volatile activity-stimulating additive from the shaped catalytic mass or particle. Usually a calcination time of about 0.1 to 24 hours using a temperature of about 800 to 1500 F., frequently near the temperature at which the catalyst actually is to be used in an oxidative dehydrogenation process, is suitable. During calcination, an ambient atmosphere can be utilized, or an inert atmosphere such as nitrogen can be utilized, if desired, though it does not appear to be necessary.

The drying and calcining steps not only remove moisture and minor amounts of volatile materials from the catalyst, thus preshrinking the catalyst so that it will not shrink further when used in dehydrogenation processess, but also serve to activate the catalyst.

The following example and runs shown therein demonstrate the effectiveness of my catalysts as prepared according to the process and method of my invention. The catalysts so prepared and the materials converted should be considered as illustrative and not as limitative of the scope of my invention.

EXAMPLE The catalytic compositions in the runs following were prepared from a phosphorus-containing tin oxide gel prepared such that the amount of phosphorus was 10 weight percent in relation to the total composition after drying and calcining. The composition was prepared by coprecipitation of a mixture of stannic chloride and phosphoric acid by the addition thereto of ammonia. The wet gel so prepared was washed with water to remove chloride, and filtered to a wet gel cake containing about weight percent water. For the control 1 as shown in Table I below approximately 1000 g. (gram) of the above-described wet gel was mixed with an additional ml. of water and homogenized. This mixture was air dried at room temperature to remove excess water, and then further dried at 350 F. for 3 or more hours. The dried material then was mixed with a minor amount of a powdered polyethylene tableting lubricant in amount equivalent to 3 weight percent based on the dried material. This mixture was tableted in several batches with varying degrees of compaction. These tablets were heated to 1200 F. at a rate of 300 F. rise per hour and maintained at 1200 F. for two or more hours, for calcination.

Runs 2, 3, and 4, exemplifying the process and method of my invention, were carried out in a manner similar as described above except that appropriate amounts of a heat-decomposable heat-volatilizable activity-stimulating salt, ammonium sulfate in runs 2 and 3 and ammonium nitrate in run 4, were added at the time the wet gel was mixed with additional water and homogenized as described above.

These catalysts then were used to convert butene to or 75 butadiene, using a single pass of butene-Z at 300 volume space velocity, a 4:1 airzbutene-Z ratio, and an 18:1 steam:butene2 ratio.

The yields in Table I above were taken from a plot of yield versus tablet strength at a tablet strength of 8 pounds. Since it is desirable to have a high strength or hard catalyst for commercial production purposes, the catalyst tablet for the runs of the invention actually were made at a high compaction so that the finished tablets were equal to the control tablets in hardness, even though it is known that higher compaction generally reduces catalyst activity. If the catalyst samples of both control run and runs 2, 3, and 4 of the invention were compared at the same degree of compaction, the results would be even more favorable.

The single pass yields given in Table I above demonstrate conclusively that the substantial increase in yield obtained by providing in the catalyst preparation a heatdecomposable heat-volatile activity-stimulating ammonium salt at a stage prior to a catalyst-forming step results in substantial increase in yields of butadiene in use of the catalyst of my invention in an oxidative dehydrogenation process.

My catalysts can be used not only in an oxidative dehydrogenation process as exemplified above, but in any oxidative dehydrogenation process in which a material to be converted is an al-kene, a cycloalkene, an alkylpyridine, or an alkyl-substituted aromatic, using elevated contacting temperatures, and a molecular oxygen-containing gas, with or without the presence of steam.

Suitable alkenes contain from 3 to 10, more usually from 4 to 6, carbon atoms per molecule, and include propylene, n-butene, n-pentene, the decenes, and the like. The alkadienes contain from 4 to carbon atoms per molecule, inclusive, such as butadiene, isoprene, and the like. The cycloalkenes contain from 4 to 10 carbon atoms per molecule, preferably from 4 to 6, such as cyclobutene, S-isopentylcyclobutene, and the like.

The alkyl aromatics and alkyl pyridines contain from 1 to 4, more usually 1 to 2, alkyl groups per ring, with the rings containing from 5 to 8 carbon atoms per ring; such alkyl-substituted pyridines or aromatics should contain at least 1 alkyl group having at least 2 carbon atoms per alkyl group. Examples of suitable materials include ethyl benzene, the nand isobutyl benzenes, hexylbenzene, ethyl pyridine, 2-ethyl-5-hexyl pyridine, and the like.

Exemplary reactions according to the process of my invention include the formation of 1,3-butadiene from the butenes, isoprene from 2-methylbutenes, styrene from ethylbenzene, furan from butadiene, and the like.

The amount of catalyst employed can vary widely depending upon materials present and the conversion and selectivity desired, though the amount chosen will be that which for the given reaction is in eifective amount to produce the desired dehydrogenation results.

The molecular oxygen-containing gas employed can be present as such, or can be utilized with inert diluents including nitrogen and the like. Suitable molecular oxygen-containing gases include air, flue gases containing residual oxygen, or other available gases of suitable nature. Substantially pure oxygen can also be employed where it is desired.

The operating conditions for the oxidative dehydrogenation process utilizing the improved catalysts of my invention can vary widely, generally include a temperature of from about 700 to 1300 F., a pressure of about 0.05 to 250 p.s.i.a., and oxygemgaseous organic compound feed volume ratio of about 0.1:1 to 3:1, and where steam is used, a steamwrganic compound feed volume ratio of about 0.1 :1 to 50:1. The organic compound feed space rate measured in volumes of organic compound vaporzvolume of catalyst:hour at 32 F. and 15 p.s.i.a. can be from about 50 to 5,000.

Processes of conversion which utilize the improved catalyst I have described ordinarily are conducted by forming a mixture, usually preheated, of organic compound feed, steam where used, and the oxygen-containing gas or gases, and passing this admixture over the catalyst composition particles at desired temperature and pressure relationships. Separation and recycle of unconverted organic compound feed can be employed where desired. Converted products obtained according to the process of my invention are useful within various processes such as polymerization and the like, such as of butadiene to polybutadiene, isoprene to polyisoprene.

Reasonable variations and modifications of my invention are certainly possible within the scope of my disclosure including the specification and claims, yet without departing from the reasonable scope and intended spirit thereof.

What is claimed is:

1. A process for oxidative dehydrogenation of at least one feed material selected from alkenes containing from 3 to 10 carbon atoms per molecule, alkadienes containing from 4 to 10 carbon atoms per molecule, cycloalkenes containing from 4 to 10 carbon atoms per molecule, alkyl aromatics containing from 1 to 4 alkyl groups per ring of which at least one alkyl group contains at least 2 carbon atoms, and alkylpyridine containing from 1 to 4 alkyl groups per ring of which at least one alkyl group contains at least 2 carbon atoms, which comprises contacting said feed material, under oxidative dehydrogenation conditions, with a catalyst composition consisting essentially of phosphorus, tin, and oxygen, said catalyst composition containing from about 0.1 to about 16 weight percent phosphorus and from about 15 to about weight percent tin;

said catalyst composition having been prepared by (1) forming a wet gel catalyst base consisting essentially of at least one tin-containing component and at least one phosphorus-containing component,

(2) admixing said wet gel catalyst base with at least one heat-decomposable, heat-volatile, activity-stimulating ammonium salt so that the resulting admixture contains from about 2 to about 2-0 weight percent of said ammonium salt based on the total weight of said catalyst composition, and

(3) calcining said admixture at a temperature in the range of about 800 to about 1500 F. for a time in the range of about 0.1 to about 24 hours to remove said ammonium salt,

said amonium salt being selected from the group consisting of ammonium carbamate, ammonium carbonate, ammonium nitrate, amonium nitrite, ammonium sulfate, and ammonium salts of carboxylic acids having up to 12 carbon atoms per molecule.

2. A process in accordance with claim 1 wherein said oxidative dehydrogenation conditions comprise a temperature in the range of about 700 to about 1300 F a pressure in the range of about 0.05 to about 250 p.s.i.a., the presence of molecular oxygen in an amount to provide a volume ratio of said molecular oxygen to said feed material in the range of about 0.121 to about 3:1, and a feed space rate for said feed material, measured in volumcs of said feed material per volume of catalyst per hour at 32 F. and 15 p.s.i.a., in the range of about 50 to about 5000.

3. A process in accordance with claim 2 wherein said oxidative dehydrogenation conditions further comprise the presence of steam in an amount to provide a volume ratio of steam to said feed material in the range of about 0.1 :1 to about 50:1.

4. A process in accordance with claim 3 wherein said feed material comprises at least one of said alkenes.

5. A process in accordance with claim 4 wherein said ammonium salt comprises ammonium sulfate.

6. A process in accordance with claim 4 wherein said ammonium salt comprises ammonium nitrate.

7. A process in accordance with claim 1 wherein said feed material comprises at least one of said alkenes and wherein said ammonium salt is ammonium sulfate.

8. A process in accordance with claim 1 wherein said feed material comprises at least one of said alkenes and wherein said ammonium salt is ammonium nitrate.

9. A process in accordance with claim 1 wherein said wet gel catalyst base further comprises at least one member selected from the group consisting of Group Ia components and Group IIa components.

10. A process in accordance with claim 9 wherein said phosphorus-containing component is a phosphoric acid, a phosphorous oxide, a phosphorous halide, a Group Ia alkali metal phosphate, or a Group He alkaline earth metal phosphate; said tin-containing component is a stannous or stannic halide, sulfate, acetate, oxide, tartrate, or nitrate; said Group Ia or IIa component is a Group Ia or IIa metal or metal-containing material, said Group Ia or IIa metal is lithium, sodium, potassium, rubidium, cesium, beryllium, magnesium, calcium, strontium, or barium, and said Group Ia or IIa metal-containing material is a nitrate, halide, sulfate, oxalate, acetate, carbonate, propionate, tartrate, bromate, oxide, or hydroxide, and wherein said catalyst composition contains from about 0.1 to about 10 weight percent of said Group Ia or IIa metal, based on the total weight of said catalyst composition.

References Cited UNITED STATES PATENTS 3,274,283 9/1966 Bethell 260-680 3,501,547 3/1970 Nolan et al 260-680 3,501,548 3/1970 Nolan et a1 260-680 3,555,105 1/1971 Nolan et al 260-680 3,580,969 5/1971 Nolan et al 260-666 2,428,910 10/ 1947 Foster 252-442 3,370,081 2/ 1968 Sennewald et a1 260-465 3,392,187 7/1968 Eden et a1. 260465.3 3,513,215 5/1970 Ogle 260-680 3,557,238 1/1971 Cunningham 260-680 3,640,901 2/ 1972 Walker 260-680 X PAUL M. COUGHLAN, 111., Primary Examiner US. Cl. X.R.

252-437; 260-290 V, 666 A, 669 R 

